The conventional motorcycle disk brake lock is generally provided with a rectangular lock body having a slot for receiving therein the disk brake. A lock bolt is put horizontally through the slot and a heat radiating hole of the disk brake so as to disable the motorcycle. Such a motorcycle disk brake lock as described above is defective in design in that the lock body of the disk brake lock is engaged with the outer edge of the disk brake when the distance between the lock bolt and the slot of the lock body is too small, and that the inner portion of the lock body can touch the motorcycle hub to preclude the lock bolt being put through the heat radiating hole of the disk brake when the distance between the lock bolt and the slot of the lock body is too great. In addition, the lock bolt can not be easily put through the heat radiating hole of the disk brake if the disk brake happens to have a small outer diameter.